size_t is the unsigned integer type of the result of the sizeof operator and the alignof operator.

Notes

size_t can store the maximum size of a theoretically possible object of any type (including array). On many platforms (an exception are systems with segmented addressing) size_t can safely store the value of any non-member pointer, in which case it is synonymous with uintptr_t.

size_t is commonly used for array indexing and loop counting. Programs that use other types, such as unsignedint, for array indexing may fail on, e.g. 64-bit systems when the index exceeds UINT_MAX or if it relies on 32-bit modular arithmetic.